1. Field of the Invention
The present invention relates to a non-self-luminous display device, and more particularly to a liquid crystal display device having a flat lighting device which includes a light guide plate on a back surface of a liquid crystal display panel and uses a light emitting element as a light source. To be more specific, the present invention relates to the light diffusion structure of the light guide plate.
2. Background Art
Recently, the liquid crystal display device has been popularly used as a display device. Particularly, the liquid crystal display device is used as a display part of portable equipment because of a reduced thickness, a reduced weight and low electric power consumption.
However, the liquid crystal display device is not self-luminous and hence, the display device requires an illumination means. In general, as an illumination device which is used for the liquid crystal display device, a flat lighting device referred to as a backlight is popularly used. Conventionally, although a cold cathode fluorescence lamp has been used as a light emitting element of the backlight, an LED has been also recently used as the light emitting element in the portable equipment.
The backlight usually includes a plate-like light guide plate. The light guide plate is made of a light-transmissive resin material, and light which is incident on the light guide plate from a light emitting element pass through the inside of the light guide plate. Reflection members, light diffusion members or the like such as grooves or projections are formed on the light guide plate, and the light which passes through in the inside of the light guide plate is radiated toward a back surface of a liquid crystal display panel by the reflection members or the light diffusion members.
For example, JP-A-2005-331565 or the like proposes a liquid crystal display device which uses LEDs as light emitting elements, arranges a plurality of LEDs on a plurality of corner portions of a light guide plate, and forms concentric arcuate inclined surfaces about the LEDs which reflect the light on the light guide plate.